Microalgae: Site-specific temperature modelling of photobioreactors
Cultivation of microalgae as biofuel feedstock is subject to international R&D efforts. In addition to light intensity and nutrient concentration, algal cell growth crucially depends on the temperature of the cultivation medium, and values exceeding 40 °C or below 0 °C can result in heavy yield losses. Detailed knowledge of the cultivation temperature as function of reactor dimensions and geographic location is therefore required.
Researchers at Bauhaus Luftfahrt have developed a temperature simulation model for an array of vertical flat panel photobioreactors (PBRs). This model is based on a balance of all relevant heat fluxes, including first-order reflections and mutual shading of reactor panels.
Application of the model for potential cultivation sites in the U.S., using local weather data covering an entire year, showed that algae cultivated in outdoor PBRs are exposed to strong temperature variations. Locations with Mediterranean climates (for example, Santa Barbara, CA) offer favourable growth conditions. In contrast, frequent occurrence of temperature peaks above 40 °C during summer times renders cultivation at very sunny and hot locations challenging (for example, Phoenix, AZ). It is important to note that mutual shading of reactor panels was found to have a great impact on the reactor temperature: High-temperature peaks are mitigated, resulting in a more homogeneous temperature profile. However, at the same time, shading reduces the intensity of photosynthetically relevant light in the reactor.
Future work will focus on coupling the developed temperature model with a specific growth model for microalgae in order to assess potential biomass yields as function of location, reactor design and plant configuration.
- Balance of heat fluxes: Heat fluxes taken into account for the temperature simulation in vertical flat panel photobioreactors. The cut-out displays the typical light distribution of diffuse sunlight within a single reactor panel.
- Temperature profiles for various climate zones in the U.S. Assumptions: North-South-orientation of panels, panel distance 0.5 m, panel thickness 0.05 m, panel height 1 m, panel length 2 m